My two cents. Don't stress about the cracks in the wood. I did the same thing when I built a coop from recycled wood about six or seven years ago. I caulked all the cracks and painted the inside and out with regular exterior house paint. Within a year, cracks appeared, but by then the chickens were already in it, and I had other things to deal with, so I just let it go. Nine years into chicken keeping, and I have never had red mites or lice. I have only had to deal with feather mites a couple of times, and those are easily dealt with, with a couple of drops of Ivermectin on the back of the neck, and don't live in the coop, I don't do anything to "prevent" mites. IMO, healthy chickens that dust bathe usually keep mites under control themselves. I have never used straw, because I have read you can bring in mites with that. I don't know if that's true, just saying. I think you have done a great job with your kind landlord's "gift" . That said, I do have a few suggestions. Your chickens don't need a ramp for that low of an entry, they will just hop up. Don't bother with one. My coop is 3 feet off the ground and my girls refused to use the ramp, coming or going, so I removed it until recently, when a couple of older girls with issues, needed a little help. We often forget, until we have them, that chickens can fly. My main concern is the run, and dust bathing. The run is good, but a little small, and the chickens need to dig and scratch and dust bathe in the dirt. Can you remove the boards in the run, and put a wire skirt around it instead? Is it possible to resurrect the fence the landlord brought for supervised out side the run time? Minus the gravel, if possible. One thing I have learned, with my years in chicken land, is that nothing is perfect, you always wish you had done something this way jnstead, and you often can't know that until you try it. There are lots of ways to do chickens, and my way may not be what works for the other guy. We can only chime in with our own experience. I love having chickens, in spite of the work! , and expense! and sometimes heartache. Jump in, and get some of the fun part.